Cell Growth & Cell Membrane – Introduction to fundamental concepts of Biological Science including the organization and common characteristics of living matters, cell structures and functions, food production by photosynthesis, harvesting energy, mechanism of cells reproduction, genetics, evolutions, and Human Biology. Introduction to general chemistry including basic concepts about matter, atomic structure, chemical bonds, gases, liquid, and solids, solutions, chemical reactions, acid, bases, and salt;
organic and biochemistry including hydrocarbons and their derivatives, carbohydrates, lipids, proteins, enzymes, vitamins, and minerals, nucleic acids; principles of physics and applications to nursing including gravity and mechanics, pressure, heat and electricity; nuclear chemistry and nuclear physics, effects of radiation on human beings, and protection and disposal. The aim of the course is to acquire knowledge and skills in general biological science, general chemistry and physics.
Cell Growth & Cell Membrane
Definition of Cell Growth:
The term cell growth is used in the contexts of cell development and cell division. When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two “daughter cells”. When used in the context of cell development, the term refers to increase in cytoplasmic and organelle volume, as well as increase in genetic material before replication.
or
Cell growth is an increase in the size of a cell. It occurs during the interphase of the cell cycle, during which both the nucleus and the cytoplasm enlarge.
Cell Membrane
Definition of Cell Membrane:
The cell membrane (also called the plasma membrane), is a thin, pliable, elastic structure which envelops the cell.
or
It is a thin elastic structure that completely envelops the cell and which forms its boundary. Its basic structure is lipid bilayer interposed with large protein molecules.
➤ Thickness: 7.5 to 10 nm.
➤ Composition: It is composed of
a) Protein: 55%
b) Lipids:
- Phospholipids – 25%
- Cholesterol -13%
- Other lipids=4%
c) Oligosaccharide: 3%
Figure: Cell Membrane
Function of Cell Membrane:
- The plasma membrane gives boundary of the cell.
- It maintains the shape of the cell.
- Maintains the structural integrity of the cell by membranes proteins,
- It separates the protoplasmic contents of a cell from those of the neighboring cells.
- It acts as a selective barrier that regulates the passage of certain materials.
- Facilitates the transport of specific molecules.
- Regulates cell to cell interactions.
- Forms a sensory surface, especially in nerve and muscle cells.
- Serves as a site of receptors.
Another Answer
Functions of the cell membrane:
➤ Protective: Outer membrane is protective to the cell.
➤ Selective sieve: It allows some particles to pass through it, while obstructs others. Lipid soluble materials pass through the non-polar lipid layer whereas water soluble materials pass through the hydrophilic (polar) protein layers.
➤ Absorption of nutrients and secretion of waste products: The nutrients of the cell enter and end products of metabolism come out of cell membrane.
➤ Gaseous exchange: Transport of O2 into the cell and CO2 out of the cell are also mediated through the cell membrane.
➤ The cell membrane in most cases helps to maintain the shape and size of the cell.
➤ Helps maintenance of internal environment within the cell
Structure of cell membrane
A cell membrane is composed of the following structures –
➤ Lipids: (40%) Membrane phospholipids have a glycerol backbone, which is the hydrophilic (water soluble) head and two fatty acid tails, which are hydrophobic (water insoluble). The hydrophobic tails face each other and form a bilayer.
➤ Proteins: (55%)
- Integral proteins:
✓ Are anchored to, and imbedded in the cell membrane through hydrophobic interactions.
✓ May span the cell membrane.
✓ Includes ion channels, transport proteins, receptors and GTP-binding proteins
Figure: Structure of a cell membrane,
- Peripheral proteins:
✓ Are not imbedded in cell membrane
✓ Are not covalently bound to membrane components.
✓ Are loosely attached to the cell membrane by electrostatic interactions.
➤ Carbohydrates: (5%) Also called glycocalyx. They occur almost invariably in combination with proteins or lipids in the form of glycoproteins or glycolipids,
(Ref by- Guyton & Hall/13th /12-14+ Linda S. Costanzo/4th/1+Sembulingam/7/4)
Chemical composition of the cell membrane:
Various compounds that make up the cell membrane-
➤ Protein-55%
- Integral protein.
- Peripheral protein
➤ Phospholipid – 25%
- Phosphatidylcholine.
- Phosphatidylethanolamine.
- Phophatidyinositol.
➤ Cholesterol – 13%
➤ Other lipid – 4%
➤ Carbohydrate – 3%
- Glycoproteins.
- Glycolipids.
- Proteoglycan.
Note: The membrane carbohydrates (glycoproteins, glycolipids & proteoglycan) are collectively called glycocalyx. In the cell membrane: Proteins: phospholipids = 1: 50
(Ref by- Guyton & Hall/13th /12)
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